Efficacy of video-otoscope-guided septum bulla fenestration and middle ear lavage for treating otitis media in cats

Abstract

Case series summary

Feline otitis media (FOM) is an inflammatory condition of the middle ear in cats. The bony septum of the tympanic bulla divides it into lateral and medial compartments, making general middle ear lavage insufficient for clearing the medial compartment. The effectiveness of video-otoscope (VO)-guided myringotomy and saline lavage of the middle ear has been recently demonstrated; however, recurrence was noted in some cases. In this study, we evaluated the efficacy and safety of VO-guided septum bulla fenestration (SBF) with lavage of the medial compartment in 31 cats (44 ears) diagnosed with FOM. The cases were retrospectively reviewed between August 2021 and November 2023. Diagnoses were based on clinical signs (eg, chronic otorrhea and vestibular signs), imaging (CT, MRI or radiography) and myringotomy findings. All cats underwent middle ear lavage followed by SBF to access the medial compartment. During myringotomy and SBF, the obtained samples were evaluated cytologically and clinical signs were monitored for at least 6 months. Significant additional effusion was drained from the medial compartment in 38 (86.4%) ears, and bacteria were identified on cytology in 5.3% of the samples. A total of 16 ears showed recurrence or persistent clinical signs; most responded to subsequent medical therapy or repeat lavage without requiring surgery. Overall, stable remission was achieved in 39/44 (88.6%) ears. No severe postoperative complications were observed; one cat had transient facial nerve paralysis and another had Horner’s syndrome.

Relevance and novel information

VO-guided SBF provided minimally invasive access to the medial compartment of the tympanic bulla, allowing lavage of otherwise inaccessible effusion. Most cases achieved stable remission, but recurrence occurred in some, indicating that SBF may serve as an adjunct therapy rather than a definitive solution. Further studies with extended follow-up are needed to clarify its long-term prognostic value.

Introduction

Feline otitis media (FOM) often arises as a result of Eustachian tube obstruction or dysfunction caused by nasal or upper respiratory diseases and may be associated with inflammatory polyps or tumours. ¹ In general, clinical signs of FOM include chronic otorrhoea and hearing loss, often accompanied by Horner’s syndrome or, less commonly, facial nerve paralysis.^{1 –3} Inflammatory discomfort may cause otalgia and pain on jaw movement and, in some cases, reduced appetite or difficulty eating due to adjacent tissue inflammation.^2,3 If otitis interna is concurrently present, head tilt and other features of peripheral vestibular dysfunction, such as ataxia and nystagmus, may be observed.^{1 –3} When associated with nasopharyngeal polyps, cats may also exhibit nasal discharge, sneezing, stertorous breathing or dyspnoea.^2,4,5 Rarely, if infection extends intracranially, more serious signs, such as seizures, central vestibular dysfunction or depressed consciousness, may occur.^1,6 Although the true prevalence of FOM is unclear, subclinical middle ear effusion is sometimes identified incidentally on imaging.

Treatment options for FOM include medical management, surgical intervention and middle ear lavage. In one study, a 73% success rate (8/11 cats) with medical management was reported, in which cats were treated for several weeks and success was defined as resolution of clinical signs without surgical intervention. ⁷ Another study reported that oral antibiotic and corticosteroid therapy successfully managed approximately 66% of FOM cases with presumptive intracranial complications. ¹ Pasteurella multocida, a common oral bacterium in cats, was isolated in 24% of these cases, suggesting that ascending infections from the oral cavity through the Eustachian tube play a role in FOM development in some cases. ¹ Consequently, although broad-spectrum antibiotics (eg, amoxicillin-clavulanate) were initially recommended in that report, ¹ current guidelines emphasise judicious antibiotic use based on confirmed infection, ideally guided by culture and sensitivity testing.^{8 –10}

Surgical management of FOM includes ventral bulla osteotomy (VBO), with total ear canal ablation and lateral bulla osteotomy typically indicated for cases with concurrent external ear disease.^{11 –14} These surgical interventions are frequently indicated for cases unresponsive to medical therapy and middle ear lavage, although definitive treatment guidelines are lacking. This approach may reflect concerns about the relatively high rate of complications associated with these procedures. In one study, VBO was reported to be successful in approximately 83% of cats with FOM; ¹¹ however, complications associated with these surgeries have been documented. For instance, the same study reported that VBO-related complications include Horner’s syndrome (68.2%, with 19.4% being permanent), head tilt (30.1%, with 22.1% being permanent) and facial nerve paralysis (13.5%, with 8.0% being permanent). ¹¹ In addition, 31% of cats undergoing VBO experienced serious adverse events, with life-threatening complications (such as major haemorrhage or respiratory distress) occurring in 8%. ¹² A newer surgical technique, transoral ventral bulla osteotomy, has been introduced as a less invasive alternative, but clinical experience and published data remain limited. ¹⁵

Recently, a combination of video-otoscope (VO)-guided middle ear lavage and medical treatment with glucocorticoids and antibiotics has been reported as a safe and effective treatment for FOM.^3,7 This method is also useful in cats that are unresponsive to medical treatment alone. However, one study reported that recurrence occurred in approximately 30% of cases within 2 months of middle ear lavage, ³ necessitating repeat lavage or surgical intervention. Unlike dogs, cats have a bony septum that divides the tympanic bulla into distinct lateral and medial compartments (Figure 1). ¹⁶ Such anatomical features could potentially contribute to the persistence or recurrence of effusion following conventional lavage, although direct evidence remains limited.

Figure 1

CT image of the feline tympanic bulla. In cats, the bony septum divides the tympanic bulla into medial (M) and lateral (L) compartments

We previously reported a case of FOM successfully treated with VO-guided SBF and lavage of the medial compartment; ¹⁷ however, a large-scale study on the efficacy and complications of this procedure is lacking. This retrospective study examined 44 ears of 31 cats treated with VO-guided septum bulla fenestration (SBF) using Kirschner wires to lavage the medial compartment.

Case series description

Materials and methods

Cats

This retrospective investigation included cats diagnosed with FOM that were initially treated with SBF and lavage by a single practitioner between August 2021 and November 2023 at 14 veterinary hospitals across Japan. Cats with malignant ear canal masses (eg, carcinoma) confirmed via histopathology were excluded. No cases with cholesteatoma or other non-inflammatory mass lesions were included. FOM diagnosis was based on clinical signs, eardrum opacity or perforation, and imaging examinations (radiography, CT or MRI). Specifically, FOM was confirmed when CT or MRI demonstrated middle ear effusion or, when imaging was unavailable, when VO revealed decreased tympanic membrane lucency and a mucoid effusion was confirmed on myringotomy. Data on signalment, clinical signs, presence and nature of effusion after fenestration, tympanic membrane regeneration, postoperative treatment, prognosis and complications were collected.

Myringotomy and middle ear lavage

To prepare for myringotomy and general middle ear lavage, the external ear canal was examined using the Tele Pack X LED system (Karl Storz Endoscopy Japan), an otoscope (Karl Storz Endoscopy Japan) and a 9.5 Fr rigid scope (Operating Telescope 30°, 9.5 Fr, length 14 cm; Karl Storz Endoscopy Japan). When cerumen was observed, a feeding tube (3 Fr; Atom Medical) was inserted through the instrument channel of the rigid scope, and saline (Otsuka Normal Saline; Otsuka Pharmaceutical) was used to gently flush the cerumen from the ear canal. Hair and cerumen debris in the ear canal were carefully removed using grasping forceps (3 Fr, length 28 cm; Karl Storz Endoscopy Japan) and the eardrum was examined. If a polyp was found in the ear canal, it was removed using either a polypectomy snare (Karl Storz Endoscopy Japan) or grasping forceps. After lavage, the eardrum was re-examined. If it was intact, myringotomy was performed using a urinary catheter (PP Catheter for Cats [tip hole]; Fujihira Industries), with its tip cut at a 45° angle, and middle ear effusion was sampled. If the eardrum was perforated, a catheter was inserted through it to collect middle ear effusion. After initial lavage into the middle ear cavity using a straight catheter directed straight through the tympanic membrane, additional flushing was performed as thoroughly as possible towards the caudodorsal aspect of the cavity using a feeding tube, until mucus discharge had ceased (Figure 2).

Figure 2

General middle ear lavage. Saline was flushed towards the caudodorsal aspect of the middle ear cavity using a feeding tube to remove residual mucus effusion, after initial anterior lavage

Septum bulla fenestration

Subsequently, all cats underwent SBF and lavage of the medial compartment. The SBF procedure involved an assistant holding the ear vertically while the operator held a 9.5 Fr rigid endoscope in their left hand to visualise the ear canal and a Kirschner wire (150 × 1.1 mm; Kirikan Yoko) fixed in a pin vice (double-headed type 0.1–3.2 mm; Annex Tool Corporation) in their right hand (Figure 3). The wire was slowly inserted alongside the rigid endoscope (Figure 4a), guided into the middle ear through the myringotomy site, directed to puncture the central and slightly ventral part of the septum, and rotated to create a small hole (Figure 4b). Subsequently, a 1.9 mm rigid endoscope (Hopkins Telescope, 1.9 mm, length 10 cm; Karl Storz Endoscopy Japan) with an inspection sheath was used to circulate saline to confirm the fenestrated area. The 9.5 Fr rigid endoscope was reinserted, and a feeding tube was passed through the fenestration into the medial compartment (Figure 4c). Saline was used to flush the area to check for additional effusion (Figure 4d). If the fenestration hole was too small to allow catheter insertion, a Steinmann pin (1.6 mm, approximately 23 cm; Kirikan Yoko) was used to enlarge the fenestration, followed by lavage with the feeding tube and saline. If tube insertion through the fenestration was difficult, a 1.9 mm rigid endoscope with an examination sheath and a forceps channel (9 Fr; Karl Storz Endoscopy Japan) was used for closer observation to facilitate lavage (Figure 4e,f).

Figure 3

Setup for the septum bulla fenestration procedure. During the procedure, an assistant holds the ear vertically, while the operator uses a 9.5 Fr rigid endoscope in their left hand to visualise the ear canal and manipulates a Kirschner wire fixed in a pin vice with their right hand

Figure 4

Steps involved in septum fenestration and middle ear lavage. (a) The wire is inserted alongside the rigid endoscope and guided into the middle ear through the myringotomy site. (b) The septum is punctured with the wire and a hole is created by rotating it. (c) A feeding tube is passed through the fenestration into the medial compartment for flushing. (d) Saline is flushed to check for additional effusion discharge. (e) A 1.9 mm rigid endoscope is used for closer observation of the fenestration. (f) Final confirmation of the fenestrated area and the eardrum is performed

Cytological examination of effusion

Effusion samples collected from the middle ear, as described above, along with effusion discharged from the medial compartment after SBF, were analysed to assess cellular components and potential microbial involvement via cytology (Figure 5). Direct smears were air-dried and stained with a Diff–Quik Romanowsky stain for microscopic evaluation of bacteria, fungal elements and inflammatory cells.

Figure 5

Viscous effusion sampling from the medial compartment after septum bulla fenestration. Effusion discharged from the medial compartment was collected for cytological examination to analyse the cellular components and potential bacterial involvement

Treatment

Most cats received postoperative systemic antibiotic therapy and systemic corticosteroid (prednisolone) therapy, as well as topical ear medications in select cases; these treatments were chosen empirically based on the authors’ clinical experience rather than specific established guidelines. The selection of systemic and topical medications, including their dosage and treatment duration, varied among cases, and detailed information is provided in Table 1. Three topical ear preparations were used: ofloxacin–ketoconazole–triamcinolone acetonide combination ear drops (Welmate L3; Meiji Animal Health), a long-acting otic product containing florfenicol, terbinafine and betamethasone acetate (Osurnia; Elanco) and enrofloxacin (Baytril 2.5% injectable solution; Elanco) diluted 1:4 with saline. Topical therapy was not uniformly applied and, in some instances, was used in addition to systemic therapy. In general, topical ear medications were avoided in cats with ruptured tympanic membranes because of the potential risk of ototoxicity; however, topical treatment was administered with informed owner consent in cases where, based on the authors’ clinical judgement, it was considered the most appropriate option despite this risk. We acknowledge that some treatment choices may have deviated from current guidelines for antimicrobial use, and the resulting variability in medical therapy is a limitation of this study. Intraoperative analgesia was administered in all cases, most commonly using buprenorphine. Postoperative analgesics were not prescribed.

Table 1

Signalment and clinical characteristics of all 31 cats

Cat	Breed	Age(years)	Clinical signs	Ear (L/R)	Diagnosis	Past MEL history	Bacteria in LC	Additional effusion in MC	Bacteria in MC	Eustachian tube patency	Adverse events	Treatment(systemic prednisolone)	Treatment(systemic antibiotics)	Treatment(ear drops)	Recurrence of OM signs(weeks until recurrence)	Remission status	Observation period (months)	Regeneration of eardrum
1	Mixed breed	1	Ear excoriation, bleeding, scratching	L	OM with IP	–	None	Abundant	None	–	None	1 mg/kg for 7 days, tapered 7 weeks	Doxycycline (2 weeks)	OKT-ED (24 days)	NR	–	32	Positive
2	DSH	9	Head tilt, nystagmus	L	OM	–	–	Abundant	None	Positive	None	1 mg/kg for 1 week, tapered 4 weeks	Amoxicillin (1 week)	–	NR	–	15	–
3	American Shorthair	7	Ear discharge	L	OM	Once	Cocci	Abundant	Cocci	Positive	None	1.1 mg/kg for 28 days, tapered 1 week	Cefovecin (8 weeks)	FTB-LAO	Failure to resolve	Persistent otorrhea	31	Negative
4	Russian Blue	3	Head shaking, ear scratching	R	OM	Once	None	Abundant	None	Positive	None	5 mg/kg for 12 days, tapered 11 weeks	Cephalexin (25 days)	–	NR	–	30	Negative
5	British Shorthair	5	Ear scratching, ear discharge	R	OM	–	None	Abundant	None	Positive	None	0.8 mg/kg for 6 days, tapered 10 days	Orbifloxacin (26 days)	–	NR	–	30	Negative
			–	L	OM	–	None	Abundant	None	Positive	None	0.8 mg/kg for 6 days, tapered 10 days	Orbifloxacin (26 days)	–	NR	–	30	Positive
6	American Curl	6	Ataxia	R	OM (RE)	–	None	Abundant	None	–	None	0.5 mg/kg for 6 days, tapered 5 weeks	Amoxicillin (4 weeks)	–	Recurrence (19 weeks)	Remission after second SBF	30	–
7	Scottish Fold	3	Rhinitis, ear discharge	R	OM	–	None	Abundant	None	Positive	None	0.7 mg/kg for 1 week, tapered 3 weeks	Amoxicillin-clavulanate (5 weeks)	–	Recurrence (5 weeks)	Remission with oral amoxicillin-clavulanate	29	Negative
			Rhinitis	L	OM	–	None	Abundant	None	Positive	None	0.7 mg/kg for 1 week, tapered 3 weeks	Amoxicillin-clavulanate (5 weeks)	–	NR	–	29	Positive
8	DSH	4	Ataxia, right head tilt, nystagmus	R	OM	–	None	Few	–	Positive	None	0.5 mg/kg for 18 days, tapered 4 weeks	–	–	NR	–	27	Positive
9	British Shorthair	6	Ataxia	L	OM	–	None	Abundant	None	Positive	None	0.4 mg/kg for 5 weeks, tapered 12 weeks	Doxycycline (2 weeks)	OKT-ED (20-week taper)	NR	–	27	Positive
10	DSH	2	Lethargy, anorexia, ear scratching, head shaking	R	OM with IP	–	Cocci, rods	Few	–	–	None	1.1 mg/kg for 7 days, tapered 4 week	Cephalexin (4 weeks)	–	Failure to resolve	Remission after second SBF	27	Negative
11	DSH	11	Nystagmus, right head tilt, ataxia, nasal discharge, anorexia	R	OM	–	None	Abundant	None	Positive	None	1.1 mg/kg for 7 days, tapered 19 week	Amoxicillin (10 weeks)	–	NR	–	27	Positive
			–	L	OM	–	None	Abundant	None	Positive	None	1.1 mg/kg for 7 days, tapered 19 weeks	Amoxicillin (10 weeks)	–	NR	–	27	Positive
12	Russian Blue	13	Ear scratching, ear canal mass, ear discharge	R	OM	Once	None	Abundant	None	Positive	None	0.7 mg/kg for 7 days, tapered 8 weeks	Doxycycline (2 weeks)	–	Recurrence (18 weeks)	Remission after fourth SBF	26	Positive
			–	L	OM with IP	Once	None	Abundant	None	Negative	None	0.7 mg/kg for 7 days, tapered 8 weeks	Doxycycline (2 weeks)	–	Recurrence (15 weeks)	Remission after fourth SBF	26	Positive
13	DSH	8 months	Ear discharge, ataxia, right head tilt, circling	R	OM with IP	–	Cocci	Abundant	Cocci	Positive	None	1.4 mg/kg for 7 days, tapered 5 weeks	Amoxicillin (44 days)	–	NR	–	26	Negative
14	Selkirk Rex	12	Head shaking, ear canal mass	R	OM with IP	–	None	Abundant	None	Negative	None	1 mg/kg for 7 days, tapered 9 weeks	Amoxicillin (4 weeks)	–	Recurrence (5 weeks)	Remission after second SBF	18	Positive
			–	L	OM with IP	–	None	Abundant	None	Negative	None	1 mg/kg for 7 days, tapered 9 weeks	Amoxicillin (4 weeks)	–	NR	–	18	Positive
15	Scottish Fold	7	Ear discharge	L	OM	Once	None	Abundant	None	–	Facial nerve paralysis	1.2 mg/kg for 7 days, tapered 1 week	–	–	NR	–	24	Positive
16	DSH	6	Ear discharge, ear scratching	R	OM with IP	–	None	Few	–	–	None	1.2 mg/kg for 1 week, tapered 1 week	Amoxicillin (2 weeks)	–	NR	–	22	Positive
17	DSH	10	Ear scratching, ear discharge, ear canal mass	L	OM with IP	–	None	Abundant	None	–	None	0.5 mg/kg for 1 week, tapered 7 weeks	Amoxicillin (4 weeks)	–	NR	–	22	–
18	DSH	6	Ear scratching, ear canal mass	R	OM with IP	–	None	Abundant	None	–	None	–	Doxycycline (1 weeks), amoxicillin (4 weeks)	OKT-ED (9-week taper) and enrofloxacin (1 week)	Recurrence (9 weeks)	Remission with OKT-ED	19	Negative
19	Norwegian Forest Cat	9	Abnormal behaviour, hindlimb ataxia	R	OM	–	None	Few	None	–	None	0.9 mg/kg for 1 week, tapered 7 weeks	Doxycycline (8 weeks)	Enrofloxacin (4 weeks)	NR	–	18	Positive
			Abnormal behaviour, hindlimb ataxia	L	OM	–	None	Few	None	–	None	0.9 mg/kg for 1 week, tapered 7 weeks	Doxycycline (8 weeks)	Enrofloxacin (4 weeks)	NR	–	18	Negative
20	DSH	11	Rhinitis, ear discharge	R	OM(RE)	Once	Cocci	Abundant	None	–	None	–	Cephalexin (3 weeks)	–	Failure to resolve	Persistent otorrhea	15	–
			Rhinitis	L	OM(RE)	Once	Cocci	Few	–	–	None	–	Cephalexin (3 weeks)	–	Failure to resolve	Persistent otorrhea	15	–
21	DSH	11	Ear scratching, ear discharge	R	OM	–	None	Abundant	None	–	None	0.7 mg/kg for 15 days, tapered 1 weeks	Cefovecin (4 weeks)	OKT-ED (1 week)	Recurrence (3 weeks)	Remission after second SBF	14	Positive
			–	L	OM	–	None	Abundant	None	–	None	0.7 mg/kg for 15 days, tapered 1 weeks	Cefovecin (4 weeks)	OKT-ED (1 week)	NR	–	14	Positive
22	DSH	5	Ear discharge, ear scratching, ataxia, ear canal mass	R	OM with IP	–	None	Abundant	None	Positive	None	–	Cefpodoxime (1 week), cefovecin (4 weeks)	OKT-ED (1 week)	NR	–	13	Negative
23	Scottish Fold	7	Ear discharge, ear scratching	R	OM	–	None	Abundant	None	–	None	0.8 mg/kg for 14 days, tapered 3 weeks	Cefovecin (2 weeks)	OKT-ED (1 week)	Recurrence (15 w)	Remission after second SBF	12	Positive
24	Abyssinian	16	Circling	R	OM	–	None	Abundant	None	Negative	None	1 mg/kg for 7 days, tapered 3 weeks	Enrofloxacin (26 days)	–	NR	–	12	Positive
25	Egyptian Mau	9	Sneezing, nasal discharge	R	OM	–	None	Abundant	None	Positive	None	0.8 mg/kg for 7 days, tapered 7 weeks	Cefovecin (4 weeks)	–	NR	–	12	Positive
			Sneezing, nasal discharge	L	OM	–	None	Abundant	None	Negative	None	0.8 mg/kg for 7 days, tapered 7 weeks	Cefovecin (4 weeks)	–	NR	–	12	Negative
26	DSH	11	Facial nerve paralysis, ear canal mass	R	OM	–	None	Abundant	None	Positive	None	0.9 mg/kg for 14 days, tapered 6 weeks	Amoxicillin-clavulanate (3 weeks)	OKT-ED (1 week)	NR	–	11	Negative
			–	L	OM	–	None	Abundant	None	Negative	None	0.9 mg/kg for 14 days, tapered 6 weeks	Amoxicillin-clavulanate (3 weeks)	–	NR	–	11	Positive
27	DSH	15	Ear discharge, hindlimb ataxia, left head tilt, lethargy	L	OM	Once	Cocci, rods	Abundant	None	Negative	None	0.8 mg/kg for 16 days, tapered 2 weeks	Cefovecin (4 weeks)	–	Failure to resolve	Persistent otorrhea	9	Negative
28	Norwegian Forest Cat	9	Hearing loss, miosis, ataxia	R	OM	–	None	Abundant	None	Negative	None	0.9 mg/kg for 22 days, tapered 11 weeks	Amoxicillin-clavulanate (8 days)	–	Recurrence (42 weeks)	Remission with oral amoxicillin	8	Negative
			Hearing loss, ataxia	L	OM	–	None	Abundant	None	Positive	None	0.9 mg/kg for 22 days, tapered 11 weeks	Amoxicillin-clavulanate (8 days)	–	Recurrence (42 w)	Remission with oral amoxicillin	8	Negative
29	Scottish Fold	1	Head shaking, ear discharge	R	OM	Once	None	Abundant	None	Positive	None	2 mg/kg for 7 days, tapered 9 weeks	Amoxicillin (11 days)	–	Recurrence (18 weeks)	Remission after second SBF	8	Negative
			Head shaking	L	OM	Once	None	Abundant	None	Positive	None	2 mg/kg for 7 days, tapered 9 weeks	Amoxicillin (11 days)	–	NR	–	8	Positive
30	Minuet	5	Nasal discharge, nasopharyngeal polyp, ear discharge	R	OM	Once	None	Abundant	None	Positive	None	2 mg/kg for 14 days, tapered 4 weeks	Amoxicillin-clavulanate (2 weeks)	–	NR	–	7	Positive
			–	L	OM	Once	None	Abundant	None	Positive	None	2 mg/kg for 14 days, tapered 4 weeks	Amoxicillin-clavulanate (2 weeks)	–	NR	–	7	Positive
31	Munchkin	4	Ear scratching, ear discharge	R	OM with IP	–	None	Abundant	None	Positive	Horner’s syndrome	0.8 mg/kg for 1 week	Amoxicillin-clavulanate (1 week)	–	NR	–	6	Positive

DSH = domestic shorthair; FTB-LAO = long-acting otic preparation containing florfenicol, terbinafine and betamethasone acetate (Osurnia; Elanco); IP = inflammatory polyp; LC = lateral compartment; MC = medial compartment; MEL = middle ear lavage; OKT-ED = ofloxacin–ketoconazole–triamcinolone acetonide combination ear drops (Welmate L3; Meiji Animal Health); OM = otitis media; NR = no recurrence; RE = ruptured eardrum; SBF = septum bulla fenestration

Follow-up evaluation

Follow-up examinations were performed at intervals of 1–4 weeks for at least 6 months after the procedure, with the schedule tailored to each case. The first author re-examined 20/31 cats, while the remaining 11 cats were evaluated by their primary veterinarians because of geographical constraints. At each follow-up visit, clinical signs were assessed and an otoscopic examination was performed to evaluate the ear canal and tympanic membrane (including evidence of regeneration). If otorrhea was present, a cytological sample was examined for inflammatory cells and bacteria. The follow-up evaluation was conducted as follows: remission was defined as no recurrence of clinical signs for at least 6 months, with no clinical signs of FOM and no otoscopic evidence of exudate. Cases that did not achieve remission were further classified as either ‘failure to resolve’ (no initial improvement in clinical signs after the procedure) or ‘recurrence’ (return of clinical signs after an initial improvement). Tympanic membrane regeneration (closure of the myringotomy perforation) was evaluated by otoscopic examination at follow-up visits.

Results

Cat characteristics

A total of 31 cats (44 ears) were included in this study (see Table 1 for results from this section). The median observation period after the initial SBF was 18 months (range 6–32). The breeds included various purebreds and domestic shorthairs. There were 18 castrated males and 13 spayed females. The median age was 7 years (range 8 months to 16 years). The affected ears included 24 right ears and 20 left ears; 13 cats had bilateral otitis media. Of the 44 ears, 12 had a history of at least one myringotomy. FOM was diagnosed using CT and MRI in six ears (three cats), CT alone in 15 ears (11 cats), MRI alone in nine ears (six cats), and radiography and VO examination without CT or MRI in 14 ears (11 cats). Inflammatory polyps were present in 11 ears (nine cats), confirmed by histopathology. In all cases where inflammatory polyps were present, the polyps involved both the middle ear and the external ear canal. Pre-existing eardrum perforation without inflammatory polyps was noted in three ears: two with a history of myringotomy and one presenting with severe ceruminous otitis externa.

Middle ear lavage and SBF procedure

All cats, including those with ear polyps, underwent external ear flushing followed by myringotomy and general middle ear lavage as intended. Subsequently, SBF was performed and abundant mucus was discharged from the medial compartment in 38/44 (86.4%) ears. Only a small amount of effusion was observed in the remaining ears.

Cytological examination of effusion

Cytology of the lateral compartment effusion revealed the presence of bacteria in 6/44 (13.6%) ears, with four showing cocci only and two showing both cocci and rods. Of these, four ears had a history of myringotomy and two ears had tympanic membranes perforated due to inflammatory polyps. Cytology of the medial compartment effusion (performed in the 38 ears with retrievable effusion) revealed bacteria in 2/38 (5.3%) ears; these two ears also showed bacterial presence in the lateral compartment. In both these cases, the bacteria observed on cytology were cocci, and no Gram staining was performed on the samples.

Eustachian tube patency

Nasal discharge during middle ear lavage was recorded in 30 ears, with 22/30 (73.3%) ears showing nasal discharge, confirming Eustachian tube patency.

Outcomes

Of the 44 ears treated, five (in four cats) did not show any improvement after the initial procedure and were considered failure to resolve. The remaining 39 (88.6%) ears initially responded to SBF, but 11 of these later experienced a recurrence of clinical signs once adjunctive antibiotic and/or corticosteroid therapy was tapered or discontinued. Among the cases that experienced recurrence, the interval until recurrence ranged from as early as 3 weeks to as long as 42 weeks after initial treatment, with a mean of approximately 17.4 weeks and a median of 15 weeks (see Table 1 for details). Of the 16 ears with failure to resolve or recurrence, six were stabilised with topical or oral treatment, five were stabilised after a second VO-guided lavage and two were stabilised after a fourth VO-guided lavage. One ear underwent VBO at the owner’s request, and two ears continued to have otorrhea but did not receive further treatment (the owners declined additional interventions). In three cats (four ears), otorrhoea persisted throughout the entire follow-up period and never resolved despite treatment. Overall, 39/44 ears (26 cats) achieved stable clinical remission with VO-guided lavage and adjunct medical therapy, without requiring surgical intervention.

Tympanic membrane regeneration was observed in 24/39 (61.5%) evaluated ears. In those ears where tympanic membrane regeneration was confirmed, healing occurred within 6 months after SBF. The precise timing of closure was not consistently documented because of the limitations of follow-up examinations and the challenge of assessing the tympanic membrane under conscious otoscopy. Furthermore, regeneration could not be evaluated in five ears. Cases with pre-existing tympanic membrane perforation unrelated to inflammatory polyps were excluded from the assessment of tympanic membrane regeneration, as these chronic perforations were not the result of the current procedure and therefore could not be used to assess postoperative healing. Cases 6 and 20 both met these criteria and were therefore excluded from the analysis of tympanic membrane regeneration. In cases 2 and 17, although rechecks were conducted by local veterinarians, the tympanic membrane could not be reliably examined, and regeneration could not be confirmed. Postoperative complications included mild facial nerve paralysis in one cat and mild Horner’s syndrome in one cat, both of which resolved within a few weeks. No major complications were observed.

Discussion

In this study, performing VO-guided SBF after standard middle ear lavage led to the discharge of substantial mucus from the medial compartment in many ears. This finding suggests that routine middle ear lavage alone does not sufficiently clean the medial compartment. However, even though SBF enabled more complete effusion removal (ie, thorough cleaning of both tympanic bulla compartments) in all cases, 16/44 ears still experienced persistent or recurrent signs of FOM. Thus, even with the expanded effusion drainage provided by SBF, approximately one-third of the ears required adjunct treatments to reach a disease-free state. This suggests that clearing the effusion from the medial compartment, while anatomically beneficial, did not on its own guarantee long-term remission. Other factors, such as Eustachian tube dysfunction, chronic mucositis, osteitis or secondary infections, may also contribute to persistent otitis despite aggressive lavage. The underlying systemic condition (eg, feline viral rhinotracheitis or malnutrition) and individual anatomical variability might also influence each cat’s response to treatment. On the other hand, although a minimum follow-up of 6 months was required for inclusion, the actual median follow-up was 18 months. During this period, 39/44 ears (in 26 cats) achieved stable remission without the need for surgical intervention. This suggests that VO-guided SBF, in conjunction with appropriate medical therapy, may offer sustained clinical benefits as a conservative treatment for FOM. However, our study did not include a control group or comparative treatment arm, and definitive conclusions about the superiority of SBF over conventional treatments cannot be made. The apparent benefit observed with SBF in avoiding further surgery should therefore be interpreted cautiously. Any perceived reduction in the need for subsequent surgical intervention remains anecdotal based on our data, and may simply reflect successful intensive medical management in these cases rather than an inherent advantage of SBF. Future prospective studies or controlled trials comparing SBF to traditional approaches are warranted to determine whether fenestrating the bulla septum truly improves long-term outcomes or reduces the likelihood of requiring salvage surgery.

Cytological examination revealed that 36/38 (94.7%) of medial compartment effusions were negative for bacteria, as were 38/44 (86.4%) of lateral compartment samples. In all ears where bacteria were observed, either a pre-existing tympanic membrane perforation or a prior myringotomy was present. These findings may suggest that bacterial infection is not a common primary aetiology of FOM, and that bacteria observed in some cases were possibly secondary contaminants associated with tympanic membrane disruption. However, as bacterial culture and sensitivity testing were not performed in this study, further investigation is needed to confirm these findings. Nonetheless, routine empirical antibiotic use for FOM may not be justified. Instead, cytology – and ideally culture and sensitivity testing – should guide antimicrobial treatment as part of an antimicrobial stewardship approach. In this study, bacterial cultures were not performed in any of the cases, which is a clear limitation. Cytology alone may have missed some bacterial infections due to its limited sensitivity, so our findings regarding the presence or absence of bacteria should be interpreted with caution. This limitation should be taken into account, and future prospective studies incorporating standardised culture and sensitivity testing are warranted to guide appropriate antimicrobial use.

The SBF procedure in this study was found to be safe, with only two transient complications observed (facial nerve paralysis in one cat and Horner’s syndrome in another); however, the lack of postoperative analgesic administration represents a potential limitation of the current protocol. Although formal pain scoring was not conducted, no overt signs of discomfort were observed during routine clinical monitoring. Nonetheless, the necessity of routine postoperative pain management should be carefully evaluated in future cases. In addition, the reproducibility of the technique may be limited by variation in middle ear anatomy (eg, septum thickness) and operator experience. Preoperative CT imaging could aid in assessing feasibility and reducing intraoperative risk.

This study has several limitations. The retrospective design and lack of culture data may limit generalisability. Subjective interpretation of video-otoscopic findings and variable follow-up intervals also introduce potential bias. In addition, not all follow-up examinations were performed by the same clinician, which could have led to inconsistencies in assessing outcomes such as tympanic membrane healing. In cases of bilateral disease, middle ear effusion was sometimes identified in the contralateral ear without clearly distinguishable clinical signs. Although all included cats presented with signs consistent with FOM, it is possible that some ears exhibited only minimal or subclinical disease. Despite these limitations, our findings suggest the utility of SBF in managing FOM and provide a foundation for further prospective, controlled studies.

Conclusions

In this retrospective study, VO-guided SBF enabled access to otherwise unreachable mucoid effusion in the medial compartment of the tympanic bulla. This permitted direct lavage of the medial compartment, highlighting the value of SBF as a less invasive, non-surgical alternative to conventional surgical management for FOM. Notably, clinical remission was achieved in most cases; however, the recurrence rate was not negligible, affecting a substantial proportion of cats. Therefore, SBF should be regarded as an adjunct rather than a definitive solution for this condition. Further studies are warranted to clarify the prognostic significance of medial compartment effusion in cats.